Analysis Case Data - Steady State Form

Access the Analysis Case Data - Steady State form as follows:

Click the Define menu > Analysis Cases command to display the Analysis Cases form.
Click the Add New Case button or highlight a previously defined analysis case and click the Add Copy of Case or the Modify/Show Case button to display the Analysis Case Data form.
Select Steady State from the Analysis Case Type drop-down list to display the Analysis Case Data - Steady State form.

The Analysis Case Data - Steady-State form is used to view and change the definition of a steady-state analysis case. A steady-state analysis case solves for the response of the structure due to cyclic loading (harmonic, sinusoidal) at one or more frequencies of interest. The structure may be damped or undamped. Frequency-dependent stiffness and damping (complex impedance) properties may be included for the Link elements.

Stiffness to Use options. Choose to solve for the response using the stiffness of the unstressed structure (the Zero Initial Conditions - Unstressed State option), or at the end of a nonlinear static or nonlinear direct-integration time-history analysis case (the Stiffness at End of Nonlinear Case option). See Stiffness to Use for more information. If you don't know what to do, choose the Zero Initial Conditions - Unstressed State option.

Load Applied options. Apply the loads from one or more load cases or built-in acceleration loads, each scaled by the same or different steady-state functions. All loads specified will be added and applied in combination.

Load Type drop-down list. Choose to apply the load as a load case or a built-in acceleration load.
Load Name drop-down list. Choose the load case name, or the direction of ground acceleration, depending on the type of load. For acceleration loads, choose direction U1, U2, or U3. See Applying Acceleration Loads for more information.
Function drop-down list. Select the name of a previously defined steady-state function that specifies the magnitude of the load as a function of frequency. The default unit function, UNIFSS, is a unit scale factor at all frequencies.
Scale Factor edit box. Enter a scale factor that multiplies the load before adding it to other loads applied. For acceleration loads, the scale factor has units of acceleration, and should be consistent with the length units currently in use. For load cases, the scale factor is unitless.
Show Advanced Load Parameters check box. Check this box to reveal the following additional columns in the applied-loads table.

Phase Angle edit box. The phase angle specifies when during a loading cycle the load acts. The loading cycle starts at zero degrees, and repeats every 360 degrees. The load varies during the loading cycle according to cosine (angle – phase), where angle is the current angle in the loading cycle, and phase is the specified phase angle. Thus loading starting at a phase angle of zero follows the cosine function, and loading with a phase angle of 90 follows the sine function.
Coordinate System drop-down list. Specify a coordinate system in which the acceleration directions are measured. See Applying Acceleration Loads for more information.
Angle edit box. Specify an angle by which U1 and U2 are rotated from UX and UY in the specified coordinate system. See Applying Acceleration Loads for more information.

Add button. To add a load to the set of applied loads, enter the load type, load name, and other parameters at the top of the table, then click Add button.
Modify button. To modify a load in the set of applied loads, click on the load in the table to select it, make any changes to the load type, load name, and other parameters at the top of the table, then click Modify button.
Delete button. To remove a load from the set of applied loads, click on the load in the table to select it, then click Delete button.

First Frequency and Last Frequency edit boxes. Specify the first (lowest) and last (highest) frequency for which the response is to be calculated. These two values may be equal if only one frequency is desired. You may specify additional frequencies of interest using the parameters below. A separate solution will be obtained at each frequency. Frequency values are given in Hz (cycles per second).
Number of Increments edit box. Specify the number of uniformly spaced frequency increments between the first and last frequency at which the response is to be calculated. The increment in frequency is given by the difference between the last and first frequencies, divided by the number of increments. Specifying a reasonable number of increments will allow you to plot the response of the structure as a frequency spectrum.
Set Additional Frequencies Click the Set Additional Frequencies button to specify other frequencies of interest that cannot be given as uniform increments. See Additional Frequencies for more information.
Hysteretic Damping parameter. Click the Modify/Show button to access the Hysteretic Damping form and specify the damping to use for the analysis.